A combustion chamber is known, for example, from EP A1 0 597 138 and U.S. Pat. No. 5,373,695.
As is explained in the introduction to the above documents, the problem of thermoacoustic oscillations is becoming increasingly significant in modern low-NOx combustion chambers of gas turbines. Therefore, the prior art has given various proposals for arranging what are known as Helmholtz dampers at the combustion chamber of a gas turbine; the configuration of these dampers, in which a damping volume is in communication with the combustion chamber via a thin connecting passage, means that they are able to effectively damp certain oscillation frequencies in the combustion chamber.
Since the frequency and amplitude of the thermoacoustic oscillations that occur in a combustion chamber are influenced by a very wide range of geometric and operational parameters of the combustion chamber, the likely oscillations in a new combustion chamber cannot be predicted with anything like a sufficient degree of accuracy. It may therefore be the case that the Helmholtz dampers used at the combustion chamber are not optimally matched to the oscillations that actually occur in the combustion chamber.
It has therefore been proposed in the documents mentioned in the introduction for the Helmholtz dampers to be completely or partially exchangeable, in order to allow retrospective changes to be made to the resonant frequency. For this purpose, a manhole is provided in the turbine casing, through which the Helmholtz dampers can be exchanged.
Drawbacks in this context are firstly that matching to a resonant frequency can only take place in stages, that it is very difficult to exchange parts of dampers or entire dampers, and that a considerable design outlay is required at the turbine casing and the combustion chamber for this exchange to be performed.